Technical Field
In general, this invention relates to a chemically unreactive method of making a film-spreading powder specifically for use in conservation of drinking water supplies in outdoor impoundments including reservoirs, canals, and the like, which combines in particles thereof organic and inorganic compounds comprising, respectively: (a.) a substantially water-insoluble constituent which is known to form an evaporation retardant monolayer or ie. thin film on the evaporating free surface of a body of water, either at rest or in motion; and (b.) a water-soluble dispersing and bulking constituent which commences separation from the monolayer-forming constituent when the powder of mixed composition is deposited on the water.
It is known in the art of forming evaporation retardant monolayers on water to employ substances which immerse, into the water, hydrophilic terminal groups at one end of certain long-chain organic molecules which at the same time extend hydrophobic hydrocarbon portions of the chains upwardly into the air in parallel packed array. Aliphatic, ie. `fatty`, alcohols such as cetyl and steryl alcohols--a.k.a. respectively: hexadecanol and octadecanol--reliably manifest that orientation and form monolayer films which slow the evaporation rate by requiring upwardly escaping water molecules to expend energy in forcing adjacent molecular chains sufficiently apart to pass between them.
Another evaporation reducing mechanism complementary to that energy barrier mechanism is also known to be operative when the evaporating water surface is not smooth, but is rippled due to either prevailing air or water currents. A change in surface properties associated with the spreading of a monolayer suppresses the ripples, and this second effect reduces the roughness factor and surface area of water exposed to air, thus undoubtedly reducing the base rate of water evaporation from a surface of given perimeter. The resulting lesser number of escaping water molecules will of course still have to pass through the energy barrier of the abovementioned chief mechanism, which is operative both when the water surface is smooth and when rippled.
Since some rippling is so commonly present in outdoor settings, it is worthwhile to provide any improvement in composition properties which can enhance the ripple-smoothing effect, so long as the chief mechanism is not jeopardized; and, among other things, the present invention involves such an improvement.
Two highly recommended texts which are entirely devoted to the subject of monolayers, their formation, and other uses, are: Insoluble Monolayers at Liquid-Gas Interfaces, G. L. Gaines, Jr., Interscience Publishers, (New York, 1966); and, Retardation of Evaporation by Monolayers, edited by V. K. La Mer, Academic Press (New York, 1962)--hereinafter cited as LA MER.
It is timely to intensify reconsideration of known techniques and compositions for evaporation suppression, in order to improve humanity's stock of drought-fighting means, because there are seems to be an ominous character to currently changing weather patterns, including droughts. The changing patterns appear to be attributable in the short-term to the El Nino warming phenomenon in the Pacific Ocean, and in an indefinitely prolonged long-term timeframe to global warming associated with `greenhouse gases` emissions. On the occassion of a global warming conference at Georgetown University on Oct. 7, 1997, the President of the United States declared that the "potential for climate disruption is real".
Against a background of such concerns, contemporary workers in the art of monolayer formation will want to give intensified reconsideration to means for improving generally familiar techniques and types of compositions useful for the conservation of water supplies. For example, there has been a long-standing need for improved means whereby evaporative losses can be reduced under more adverse conditions of wind, and of water currents, than those under which prior art workers were able to establish and maintain effective monolayer films. Also, it seems noteworthy that by comparison to the amount of reservoir coverage work reported in the literature, film formation on running bodies of water has been relatively neglected, though attention to this matter is warranted by such facts as that millions of Californians depend on water supplies which course for hundreds of miles in uncovered channels traversing arid or semi-arid distincts where evaporative losses are high.
Because the present invention relates to a powder, it may seem natural to expect that the chief problem with wind where powder is used must be that wind is apt to blow the powder uselessly away from the water surface one is intending to cover. That deserves consideration in the context of equipment and techniques of distribution, but is not so great a problem--nor nearly so recalcitrant--as problems which concern adverse wind effects not on powder before it reaches the water surface but on a film after its initial formation on the water, during the stage when it should be spreading, and/or after coverage of a substantial area has already been attained. Tangential drag force due to wind affects monolayers indiscriminately, whether the composition applied to the water is initially distributed in either a solid-phase or liquid-phase state.
Light surface winds no greater than about two to five mph are viewed as initially helpful in establishing the desired full coating of a reservoir, and a common practice has been to distribute a monolayer-forming substance on water along an upwind shoreline, taking advantage of a drift effect which assists the spreading film to more quickly reach the opposite shoreline than with zero wind assistance. Ideally, the windspeed should drop and/or wind direction reverse, once the drilling has taken a film far enough downwind. Wind is rarely that cooperative, and as the Australian researcher R. G. Vines has explained with regard to a mode of wind-caused film coverage loss called `retraction`; "a monolayer, bounded downwind by a shoreline, is compressed by the wind and collapses." (LA MER, p. 147) The terms `compression` and `collapse`, in the art jargon, do not refer to vertical reduction of thickness but to reduction of the plane area covered by the monolayer produced by a given quantity of film-forming substance. The area covered when an aliphatic alcohol monolayer is most highly resistant to evaporation through it, because it is in a `condensed` state, corresponds to an optimal degree of compression.
Over-compression to the point of film collapse reduces the net gain of the condensed state effect by causing an actual reduction of the area covered, and this is often what happens in the field, due to wind. Also, the spreading and/or respreading by monolayers at varying `film pressures` (in the plane of the monolayer, not normal to it) is a rather complicated function of many factors, including: hydrocarbon chain length of substances used; polymorphism of the higher alcohols which show three or possibly more different crystal forms; history of materials preparation and storage; the temperature of the body of water; even its pH sometimes; and, convection events or currents in the water, when present. One ambitious attempt to take all such matters into account is found in a doctoral dissertation I supervised, entitled: An Investigation of Monolayer Spreading Speeds at the Air-Water Interface, by A. I. Feher, University of Victoria (1975). Unfortunately, when all of the foregoing and even other factors are theoretically favorable to spreading, a wind may rise or change direction, and either outright defeat a film-forming effort, or else incur high costs due to an increase of the volume of film-forming material distributed in excess or on a continuous basis in an attempt to make up for film losses caused by high wind and usually attendant wave action.